In the Straits of Mackinac on the Great Lakes, two tugboats clear a path through the ice for commercial shipping traffic on April 6, 1992. Leading the way is Biscayne Bay (WTGB-104), followed closely by Katmai Bay (WTGB-101). These cutters are part of the U.S. Coast Guard’s Bay-class fleet, which has remained in continuous service since 1979.
The Coast Guard operates a range of icebreakers, including one heavy and two medium vessels in the polar fleet, as well as more than two dozen smaller vessels with icebreaking capability. Among them, the Bay-class tugboats are the only icebreakers dedicated solely to domestic icebreaking missions, tasked with keeping shipping lanes on the Great Lakes and other U.S. waterways open during the cold months. All nine vessels in the fleet, numbered WTGB-101 to WTGB-109, were built between 1977 and 1987, the first five by Tacoma Boatbuilding and the last four by Bay City Maine Inc.
Designed to replace the Coast Guard’s aging 110-foot harbor tugs, the 140-foot Bay-class vessels have stronger icebreaking hulls, wider beams, greater horsepower and increased fuel capacity. They also have twice the cruising range of the older tugs, so they can stay underway for seven days. Two Fairbanks-Morse diesel engines push the vessels to a top speed of 14.7 knots.
Each vessel also has a bubbler system that pumps air along the hull to reduce friction and increase efficiency in the ice. At continuous speed, the tugs can break freshwater ice up to 20 inches thick. They can break ice up to 3 feet thick while backing and ramming, and take on pressure ridges up to 8 feet thick.
Katmai Bay was the first of the class to enter service. Laid down November 1977 and commissioned in January 1979, she was assigned to Sault Ste. Marie, Michigan, where she remains stationed today. Biscayne Bay followed as the fourth vessel in the class, commissioned in December 1979. She has spent her entire career based at St. Ignace, Michigan, working the Straits of Mackinac. Her area of operations includes the waters around Mackinac Island and the Mackinac Bridge, the northern reaches of Lakes Michigan and Huron, and sometimes Lake Superior, Lake Erie and their connecting rivers.
The Bay-class fleet remains fully in commission today, with six of the nine cutters stationed on the Great Lakes. The vessels have now served well beyond their planned 30-year service life. To keep them operational for another 15 years, the Coast Guard launched a Service Life Extension Program that upgraded their propulsion, electrical and navigation systems; replaced key components such as the bubbler system and the boat-launching davit; and modernized living quarters. Katmai Bay had a refit in 2018 and returned to the Great Lakes that year. Biscayne Bay was the final vessel to complete the program, returning to St. Ignace on August 8, 2020.
November 2025
